We study meiosis because it is itself a biologically interesting and important process, but also because it serves as a tractable model for the complex cellular changes that accompany many types of differentiation. We are interested in understanding the fundamental mechanisms by which a cell achieves such changes. Towards this end, we use high-throughput and classical genetic and molecular approaches in budding yeast (S. cerevisiae) to study the role of pervasive short protein synthesis in meiosis, specialized regulation of meiotic translation, and the role of several prominent and diverse stress response pathways in driving cells through the meiotic program.

Previous work

In my post-doctoral studies, I globally probed the regulation of the comprehensive cellular restructuring underlying meiosis. Ribosome profiling, the deep sequencing of ribosome protected mRNA fragments, is a new method that monitors protein synthesis with scale, speed, and accuracy rivaling approaches for mRNA measurement (Ingolia et al., Science 2009). I applied this method to numerous time points through the yeast meiotic program in parallel with mRNA-seq and molecular staging to generate a rich atlas of meiotic events and gene expression and the first high-resolution map of protein synthesis through a developmental program (Brar et al., Science, 2012).

What is ribosome profiling? Nuclease digestion of translating ribosomes protects only mRNA regions (footprints) being actively decoded by the ribosome (Steitz, Nature, 1969; Ingolia et al., Science, 2009). These footprints can be collected in vivo from cells and sequenced to define coding regions and quantify new protein synthesis. Shown is a comparison of the method with mRNA sequencing, which defines the positions of full transcripts, but cannot specifically identify coding regions.

This study revealed an unprecedented view of the molecular events underlying diverse aspects of meiotic biology and uncovered numerous new and dramatic instances of dynamic translational regulation through meiosis. The effort also yielded several fundamental surprises with broad significance. Projects in the Brar lab are based on exploring the basis and molecular significance of these discoveries.

A global view of meiotic protein synthesis. Ribosome footprints over each S. cerevisiae gene are shown as columns. Each time point is shown as a row, with 25 meiotic timepoints shown and two mitotic (exponential) controls. Cartoons on the left show progression through meiosis. Note the variety of patterns of regulation of protein synthesis through meiosis, with nearly every gene in the yeast genome expressed and highly regulated. This regulation is mediated by both transcriptional and hundreds of newly identified examples of dramatic translational control. At the right are more detailed views of two genes, with both mRNA and ribosome footprints shown on pooled genome browser tracks. Note that SPS1 and SPS2 show similar patterns of mRNA abundance, but very different translation patterns, reflecting just one of these examples of strong translational control.

Ongoing projects in the Brar lab

Discoveries from this study have motivated several research directions in our lab, focused on answering fundamental questions about gene regulation through meiosis.